<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>显示隐藏文本框内容</title>
  <style>
    input {
      color: #999;
    }
  </style>
</head>
<body>
  <input type="text" value="手机">
  <script>
    // 1.获取元素
    var text = document.querySelector('input')
    // 2.注册事件 获得焦点事件 onfocus
    text.onfocus = function () {
      // console.log('得到了焦点');
      if (this.value === '手机') {
        this.value = ''
        this.style.outlineColor = 'pink'
      }
      // 获得焦点需要把文本框里面的文字颜色变黑
      this.style.color = '#333'
    }
    // 3. 注册事件 失去焦点事件 onblur
    text.onblur = function () {
      // console.log('失去了焦点');
      if (this.value === '') {
        this.value = '手机'
      }
      // 失去焦点需要把文本框里面的文字颜色变浅色
      this.style.color = '#999'
    }
  </script>
</body>
</html>